Regulation of nitric oxide synthase induction by iron and glutathione in asbestos-treated human lung epithelial cells

Our plain-English summary of Regulation of nitric oxide synthase induction by iron and glutathione in asbestos-treated human lung epithelial cells, by S.H. Park, A.E. Aust (Archives of Biochemistry and Biophysics, 1998).

The study

• Authors: S.H. Park, A.E. Aust
• Journal: Archives of Biochemistry and Biophysics
• Published: 1998;360(1):47-52
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Treatment of human lung epithelial (A549) cells with crocidolite asbestos resulted in the induction of the inducible form of nitric oxide synthase (iNOS), production of NO, and a dramatic decrease in intracellular reduced glutathione (GSH). Iron, mobilized from the crocidolite fibers (27% iron by weight), and the formation of NO were required for the formation of 2'-deoxy-7-hydro-8-oxoguanosine in the DNA of the A549 cells, but not for the decrease in GSH. Therefore, we investigated the role of GSH and iron in the induction of iNOS in A549 cells by crocidolite. Iron was required for the induction of iNOS by crocidolite. A fivefold higher amount of chrysotile asbestos (3% iron by weight) was required to cause a similar decrease in intracellular GSH and induction of iNOS. In the absence of asbestos, treatment with either buthionine sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase, or ferric ammonium citrate (FAC), a soluble form of iron, did not result in induction of iNOS. However, iNOS was induced when A549 cells were treated simultaneously with BSO and FAC. The presence of 5 mM N-acetylcysteine prevented induction of iNOS in crocidolite-treated A549 cells. These observations suggest that the induction of iNOS resulted from a decrease in intracellular GSH and the presence of iron from the asbestos fibers.

Copyright 1998 Academic Press.

In plain English

This laboratory study grew human lung epithelial cells (the A549 cell line) and exposed them to crocidolite or chrysotile asbestos for 24 hours. The authors measured glutathione, a protective substance inside cells, and checked whether the cells switched on the gene for inducible nitric oxide synthase (iNOS), an enzyme that makes nitric oxide. Crocidolite lowered glutathione by 60 or 75%, depending on dose, and switched on iNOS. Crocidolite treated to remove its redox-active iron still lowered glutathione but did not switch on iNOS. Partly lowering glutathione with a drug (BSO), or adding soluble iron alone, did not switch on iNOS, but the two together did. Nearly complete glutathione depletion with BSO alone also switched on iNOS. The compound N-acetylcysteine blocked iNOS induction by crocidolite. Chrysotile needed a fivefold higher dose than crocidolite to cause a similar fall in glutathione and to switch on iNOS. The authors suggested that, in crocidolite-treated cells, iNOS induction resulted from a decrease in glutathione together with iron from the fibers. They said the role of N-acetylcysteine required further investigation. No people or animals were studied.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) experiment on cultured human lung cells
• Who was studied: Human lung epithelial type II cells (A549 cell line) bought from the American Type Culture Collection and studied at Utah State University. No human subjects or animals were studied.
• Exposure: Crocidolite asbestos (27% iron by weight), crocidolite treated with desferrioxamine B to remove its redox-active iron, and short-range chrysotile asbestos (2 to 3% iron by weight), each for 24 hours. Comparison treatments were buthionine sulfoximine (BSO, which lowers glutathione), ferric ammonium citrate (a soluble iron compound) and N-acetylcysteine. Doses are printed as 3 or 6 mg/cm2 crocidolite and 6 or 30 mg/cm2 chrysotile.
• Main results:
  • In crocidolite-treated cells, glutathione fell by 60% at the lower dose and by 75% at the higher dose, compared with untreated cells. Both doses switched on iNOS.
  • Partly lowering glutathione with BSO, to about the level seen after the lower crocidolite dose, did not switch on iNOS. Near-complete depletion with a different BSO concentration did switch it on.
  • N-acetylcysteine (5 mM) prevented iNOS induction by crocidolite, but it did not raise the cells' thiol levels. Given alone, it lowered them (by about 34%, as reported) without switching on iNOS.
  • Crocidolite with its redox-active iron removed still lowered glutathione but did not switch on iNOS (Table II).
  • Soluble iron (ferric ammonium citrate) alone neither lowered glutathione nor switched on iNOS. Combined with BSO to lower glutathione, it switched on iNOS.
  • Chrysotile at the lower dose caused a modest glutathione decrease and no iNOS induction. At five times that dose it caused a 70% glutathione decrease, similar to the higher crocidolite dose, and switched on iNOS.
  • Crocidolite did not increase the oxidized form of glutathione in the cells.
• The authors' conclusion: The authors suggested that switching on iNOS resulted from a decrease in glutathione combined with iron from the asbestos fibers. They proposed that, if this happens in the body, it may contribute to events leading to bronchogenic carcinoma (lung cancer).
• Limitations the authors state:
  • The authors found the low thiol levels in cells given N-acetylcysteine puzzling and said its role required further investigation.
  • The glutathione assay measures all soluble non-protein thiols, so N-acetylcysteine itself could contribute to the measured values.
  • The findings come from cultured cells. The authors framed any relevance to cancer in people as conditional on the same thing happening in the body.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite.

Medical terms in this study, explained in our Lexicon: Glutathione (GSH), Crocidolite, A549 Cells, Chrysotile.

Related studies

• Simian virus 40 infection down-regulates the expression of nitric oxide synthase in human mesothelial cells — E. Aldieri, S. Orecchia, et al. (2004)
• Modulation of DNA single-strand breaks by intracellular glutathione in human lung cells exposed to asbestos fibers — A. Puhakka, T. Ollikainen, et al. (2002)
• Participation of nitric oxide and iron in the oxidation of DNA in asbestos-treated human lung epithelial cells — C.C. Chao, S.H. Park, et al. (1996)
• Dual role of inducible nitric oxide synthase in acute asbestos-induced lung injury — M. Dörger, A.M. Allmeling, et al. (2002)
• Expression of inducible nitric oxide synthase in healthy pleura and in malignant mesothelioma — Y. Soini, K. Kahlos, et al. (2000)
• Early inflammatory response to asbestos exposure in rat and hamster lungs: role of inducible nitric oxide synthase — M. Dörger, A.M. Allmeling, et al. (2002)

Browse more research in Archives of Biochemistry and Biophysics, or return to medical research.